As a method for manufacturing non-fired pellets by hardening green pellets without firing through carbonation of a carbonating binder contained in the green pellets, a method for manufacturing non-fired pellets is disclosed in Japanese Patent Provisional Publication No. 50-45,714 dated Apr. 24, 1975, which comprises:
supplying green pellets containing a carbonating binder into a reactor; and blowing a carbonating gas containing carbon dioxide gas and having a prescribed temperature into the reactor to bring the carbonating gas into contact with the green pellets in the reactor to carbonate the carbonating binder contained in the green pellets, thereby hardening the green pellets to manufacture non-fired pellets (hereinafter referred to as the "prior art").
However, the above-mentioned prior art involves the following problems:
(1) Carbonation of the carbonating binder contained in the green pellets requires water and heating of the green pellets. In the prior art, the above-mentioned carbonating binder is carbonated by means of water contained in the green pellets and heating of the green pellets by the carbonating gas at the prescribed temperature. However, when the water content in the green pellets is decreased by heating of the green pellets, the carbonation of the carbonating binder is delayed and this leads to insufficient hardening of the green pellets, thus making it impossible to manufacture high-strength non-fired pellets in a short period of time.
(2) If too much water is contained in the green pellets to promote carbonation of the carbonating binder, on the other hand, there is posed another problem of collapsing or sticking of the green pellets in the reactor. Collapsing or sticking of the green pellets, if caused in the reactor, not only reduces the product yield but also causes adhesion of sticking green pellets onto the inner surfaces of the side walls of the reactor. As a result, when continuously supplying the green pellets into the reactor to continuously manufacture the non-fired pellets, smooth travelling of the green pellets through the reactor is impaired, finally making it impossible to manufacture the non-fired pellets.
For these reasons, there is a strong demand for the development of a method and an apparatus for continuously manufacturing high-strength non-fired pellets excellent in quality at a high yield in a short period of time, which, when continuously supplying green pellets containing a carbonating binder into a reactor, and blowing a carbonating gas containing carbon dioxide gas and having a prescribed temperature into the reactor to bring the carbonating gas into contact with the green pellets and to carbonate the carbonating binder contained in the green pellets, thereby hardening the green pellets to manufacture the non-fired pellets, promotes carbonation of the carbonating binder to harden the green pellets without causing collapsing or sticking of the green pellets in the reactor. However, such method and apparatus have not as yet been proposed.